Pterodactyls in the Mesozoic: A Flap in Time Frederic Jueneman Contemporary Revisoin In the mid-19th century, the British anatomist Sir Richard Owen speculated that the flying pterodactyls needed a more dense atmosphere in which to navigate. Moreover, he also thought the airmass would have to have contained elevated concentrations of carbon dioxide and reduced oxygen as compared to today's levels.^[1] Just a few years ago, the aeronautical engineer Paul MacCready -- the designer of the Gossamer aircraft that was successfully flown nonstop around the globe, refueling while continuously airborne -- attempted to physically recreate the flying machine of the late Mesozoic Era, the pterodactyl, known taxonomically as Quetzalcoatlus northropi. MacCready used modern lightweight materials such as aluminum and mylar in the construction of his mechanical flapping contrivance, which moved me to facetiously rename his artifact as Q. alcoa-duponti. The first try was a disaster, while subsequent attempts were more successful. Nonetheless, these flights were awkward and lacked regulated control. In one sense these attempts were to disprove the idea long held by some paleontologists that pterodactyls (meaning "wing finger") were gliders, unable to fly because of their unusual body size and weight. The largest known adult fossils had wingspans of 12-15 meters (40-50 feet), comparable to today's small aircraft, and estimated weights ranging from 23-50 kilograms (50-110 lbs.).^[2] Around 1985, using computer simulations, two Canadians, paleobiologist Dale Russell of the National Museum of Natural History and aeronautics engineer Parvez Kumar, determined that Quetzalcoatlus could indeed fly by flapping its ungainly bat-like membranous wings in an atmosphere at least 50% more dense than what we presently experience on Earth. Kumar and Russell's study started a chain of reasoning that may have some far-reaching significance with respect to that day and age. At this point it is appropriate to inject the demurral that the old view in which our present world order is pretty much as it was back in the primordial past is rapidly being eroded away. Although I'm a devout secular atheist myself, and don't believe in evolution as it is being currently purveyed, there are quite a few hard-won pieces of information gleaned over the years that one must use in order to build a scientific case. Without such a basis, everything is just space gas, no matter how substantive the original premises seemed to have been. Future disclosures will eventually correct our errors. Hand-waving without evidence doesn't cut it. So, with the ongoing erosion of much of 19th and early 20th century thought on Earth's primordial past -- and, of course, the not so ancient past -- we're also uncovering some "fossil" thoughts from the 19th century and earlier that were apparently right on the money, but which were not in vogue at the time or conflicted with received wisdom from the then movers and shakers in scientific inquiry. An Extremely Brief History of Earth The geological and paleontological history of our planet is divided into three major eons and various subdivisions of eras, periods, and epochs. The oldest is the Archean ("ancient") Eon that began some 4.55 billion years ago (Gya), and is generally thought to have been inanimate and devoid of any lifeforms while Earth was still cooling from its torrid cosmic birth pangs. The first adaptable invertebrates ostensibly appeared about two billion years later (2.5 Gya) during the Proterozoic ("before life") Eon, but diversity among plants and animals didn't take hold until after the beginning of the Great Phanerozoic Eon some 540 million years past, and which continues down to our own time. The Phanerozoic ("visible life") itself is divided into the Paleozoic ("early life"), Mesozoic ("middle life"), and Cenozoic ("recent life") Eras. The dozen or so periods from the Precambrian to the Quaternary Period, along with their various epoch prefixes as "Upper," "Middle," and "Lower" when dealing with geologic ages, and "Early," "Middle," and "Late" when treating paleontological histories, down to the glacial Pleistocene Epoch and the current Holocene, all comprise subdivisions of these eras. The fascinating Carboniferous Period was sandwiched between the Devonian and Permian during the latter, or "Upper" half, of the Paleozoic Era, where plantlife thrived almost uncontrollably, evidently laying down the thick coal seams and oil pools which we mine and exploit today.^[3] This unruly and rampant growth in the warm greenhouse of the Mississipian and Pennsylvanian Epochs during the Carboniferous bespeaks massive amounts of carbon dioxide in Earth's early atmosphere to permit such frenzied photosynthesis. We shall, however, concern ourselves primarily with the Mesozoic Era, that itself is divided into the Triassic, Jurassic, and Cretaceous ("chalk-like") Periods, an era which was singularly and uniquely the Age of Dinosaurs. Here, too, substantive coal beds were laid down by rampant vegetation and the calcium carbonate skeletons of microscopic foraminifera built up massive chalk and limestone formations that also indicated elevated levels of available carbon dioxide to stimulate plant growth, as well as the development of shell-like outer coverings of invertebrate lifeforms such as the early molluscs. The subsequent Cenozoic Era was the Age of Mammals, in spite of traces of mammalian existence as far back as the Late Permian or Early Triassic; and, whatwith the extinction of the dinosaurs at the close of the Cretaceous, the door opened wide for the advance and development of these furry viviparous animals. What's in a Name Velociraptor Velociraptor, which, despite Steven Spielberg's entertaining accuracy of dinosaurs, did not thrive during the Jurassic but in the Late Cretaceous. (Illustration by Bob Giuliani.) The term dinosaur itself is a hybrid of the Greek words, deinos ("terrible") and sauros ("lizard"), and was coined in 1842 by Owen in his report to the British Association for the Advancement of Science. Owen was one of the first to recognize that a new family of extinct species had once existed on the primordial Earth. He thus initiated an unflagging interest in the fossils of ancient monsters which has burgeoned in recent days with Steven Spielberg's films which attempt, in entertaining fashion, to authenticate the appearance and behavior of dinosaurs. (It might be pointed out in the interest of misplaced scholarship that the popular Velociraptor flourished in the Late Cretaceous and not, as in Spielberg's epics, in the Jurassic. Neither is it probable that Dilophosaurus spit sticky gooey-glop at its victims.) Today we have characterized dinosaurs pretty much by what they are and what they are not. However, even here, there are contradictory opinions. One source, David Norman of the Sedgwick Museum of Geology at the University of Cambridge, says that there are four identifying characteristics: Dinosaurs lived only in the Mesozoic Era; they lived only on land; they walked upright; and they were all reptiles.^[4] And, as reptilian animals, they are unique unto themselves and are not related to fish, fowl, or mammals. However, there is a genetic line through the early coelurosaurs ("hollow-boned lizards") from which birds are assumed to have evolved, although this has been seriously debated for the past century. In fact, the most heated debate revolves around whether dinosaurs were endothermic ("warm-blooded"), as per the iconoclastic Robert Bakker of the University of Colorado Museum of Natural History, rather than reptilian, or ectothermic ("cold-blooded"),^[5] despite their scaly appearance and egg-laying proclivities. As it is, few have cogently challenged the acknowledged life and death of dinosaurs exclusively in the Mesozoic, though there are numerous other clashes of persuasion that we shall not go into here. There are two major orders of dinosaurs, the saurischia ("lizard-hipped") and the ornithischia ("bird-hipped"), based on the hip-socket arrangement of the leg joint. Not all of the hundreds of fossil specimens fit easily into these two categories, nor are there hard-and-fast rules separating the more subtle family distinctions. There's even resistance toward affording a full-fledged status of Class Dinosauria to these creatures, although several authors have used the classification. Further, the evolution of contemporary birds is presumed to have come from the legacy of the saurischian theropods rather than from the bird-hipped ornithischians. These theropods, incidentally, include the notorious Tyrannosaurus rex and its voracious cousins. Archaeopteryx Archaeopteryx -- believed to be a precursor of modern birds. Such characterization, however, leaves all the sea-going creatures as ichthyosaurus and plesiosaurus out of the definition of dinosaurs, as well as -- for the purposes of this argument -- the airborne pterosaurus. The bird-like Archaeopteryx ("ancient wing"), originally found in 1862 in the Upper Jurassic foraminiferan limestone deposits near Solnhofen, Bavaria, is thought to be a precursor of modern birds, and not even remotely related to pterosaurs. There are some six additional examples of this crow-sized feathered dinosauria which have been found since then. Archaeopteryx is classified as saurischian, because of its close physical relationship to its non-feathered theropod counterparts, such as Compsognathus ("pretty paw"), along with T. rex. But feathered Archaeopteryx is not associated with the pterodactyl by any means, which latter had membranous web-like wings not unlike modern bats,^[6] and which thus far has defied consensual classification into one or another order of the dinosaur categories, and sometimes is given its own taxonomic order. Vertebrate paleontologist Adrian Desmond of Harvard has argued for a Class Dinosauria, to include ornithischians, saurischians, birds, and pseudosuchians ("false crocodile"), as well as for a separate Class Pterosauria.^[7] "The Mesozoic animals that play a crucial role in the present thesis -- dinosaurs, thecodonts ["encased teeth"] and pterosaurs -- are still officially termed reptiles. The reptilian class was originally erected to house the living snakes, lizards and turtles long before the reemergence of the Mesozoic saurians of the early 19th century. As such, the reptiles were, by definition, cold-blooded with a scaly covering and sprawling limbs, unable to sustain energetic activity, and generally confined to climatically equable regions. [Baron George] Cuvier justified the inclusion of pterodactyls, and Owen the dinosaurs, on the basis of some apparently lizard-like bones in the fossil skeletons. Given the state of contemporary knowledge, this attempt to ally past and present lifeforms was laudable for its heuristic value."^[8] Desmond's pleas haven't fallen on deaf ears, as most paleontologists are cognizant of the problems of classification, but it seems that no one wants to take the next -- albeit tricky -- steps in initiative to close the gaps in classifying extinct species. This is particularly problematic when it isn't known how many thousands of species were rendered extinct without any trace of fossil evidence of their former existence. The current popularization of dinosauria in books and films has engaged the public, but also enraged many paleontologists, but the American Museum of Natural History in New York has catered to the former, knowing full well where its priorities lie. Moreover, as paleontology has only the self-admitted pretense of being an exact science, there is enough disagreement among colleagues to keep the arguments going for some while to come. Tieing up Loose Ends Pterodactylus Pterodactylus. (Illustration by Bob Giuiliani.) The science of paleontology often goes hand-in-hand with geology to define the periods in which fossils are found. Occasionally, too, chemistry is involved, as when chemist Walter Alvarez and his colleagues at UC Berkeley investigated a thin rock layer near Gubbio, Italy, and, along with his Nobel-laureate father, Luis Alvarez, unexpectedly found what is now called the "iridium" anomaly in this layer separating the Cretaceous from the Tertiary Periods -- the K-T boundary which demarcated the Great Extinction some 65 million years ago,^[9] although some split scholarly hairs and say 66 Mya. (The "K" in K-T, by the way, is from the German Kreide, meaning "chalk.") Iridium is one of the noble metals of the platinum group of elements that is relatively rare in terrestrial deposits, but appears commonly in trace amounts in stony meteorites. This was theorized as being evidence for a meteoric impact that brought the Age of Dinosaurs to a close. Confirmation came with samples sent to Alvarez, collected by Russell from New Zealand, with additional sediments from Denmark, and subsequent finds of iridium presence at the K-T boundary elsewhere around the world. Geological, gravimetric, and magnetic investigation has recently identified the Chicxulub Crater in northern Yucatan as the most likely impact site of the primary bolide, and the story behind this investigation is a tale in itself.^[10] As Desmond said: "It is of great significance that no large-bodied animals survived the Cretaceous: the small inherited the earth."^[11] However, Desmond wrote before the Alvarez announcement and thus was unaware of its implications, describing instead the then current thinking of a hypothetical supernova explosion in our galactic neighborhood. (Ensuing considerations showed that other signature elements from a supernova outburst were missing, so this explanation has since been generally discarded.) Conversely, Bakker himself does not buy into the bolide hypothesis, opting for incipient extinctions that were merely punctuated by the meteoric impact. Others point to volcanic eruptions as sources of iridium, finding little evidence of dinosaur presence close to the critical K-T boundary line in many locations. However, fossils are discovered where you find them and not where you expect them to be. Writing in the 1950s and early 1960s, Edwin H. Colbert of the America Museum of Natural History was not privy to the future knowledge of plate tectonics and only paid lip-service to continental drift as it was then known.^[12] Colbert himself had made important discoveries in New Mexico, finding an entire quarry of a Late Triassic species in a red mudstone formation.^[13] And, in contrast to many of his colleagues as to the age of dinosaurs, despite adhering to an early date for reptiles in the Permian Period, he stated: "The dinosaurs give strong evidence for an Upper Triassic age, because it is generally considered (although one can never be completely sure of such things) that the dinosaurs did not arise from their thecodont ancestors until about the beginning of the late Triassic time."^[14] Robert Bakker, at the University of Colorado, and Peter Galton of the University of Bridgeport, and, independently, the Argentine paleontologist José Bonaparte of the Museum of La Plata in Buenos Aires, pointed to Lagosuchus ("rabbit-crocodile") of the Middle Triassic as the most likely progenitor of the dinosaurs, and as the archetypal epitome of proto-mammal and proto-pterodactyl.^[15] This rabbit-croc had the necessary light build and long legs, along with the almost universal dinosaur and pterodactyl signature of a missing collarbone. The dominance of dinosaurs over other animal lifeforms has been estimated -- depending on the source -- as ranging from 130 to 200 million years. And, in that time frame, many species of dinosaurs arose, developed, and faded into extinction. Of the hundreds which are presently known from the fossil evidence, it is thought that additional thousands of species existed at one time or another throughout the Mesozoic. Some estimates have entire families evolving every four million years into new generic family lines. The pterosaurus, first discovered in 1784 in limestone deposits in Germany and given its name in 1806 by George Cuvier, itself comprised many examples ranging from the early pigeon-sized long-tailed dimorphodon ("two sets of teeth") of the Upper Triassic to the gigantic short-tail ornithocheir and pterodactyl at the close of the Cretaceous. One reconstructed fossil found recently in Texas was estimated as having a wingspan of 20 meters (63 ft.) and weighing some 55 Kg (120 lbs.)! In the late 19th century, these creatures were considered somewhere between bats and birds but not closely related to either, since none of these Cretaceous pterodactyls, including pteranodon ("wing -- no tooth") found in Kansas, appear to have had the clavicle or collarbone hallmark of mammals. Even Archaeopteryx had such a furcula, although its order and family compatriots either had a rudimentary clavicle or none at all. In the 1870s, Thomas Huxley -- Darwin's "bull-dog" -- inter alia, had pointed out that dinosaurs and birds shared structural similarities, particularly among the smaller Compsognathus. And, the doyen of descriptive paleontology, Harold G. Seeley, of King's College in London, who separated the dinosaurs into the two orders, ornithischia and saurischia, wrote a definitive study of these flying creatures.^[16] But, because no such furcula (collarbone) had been found in the dinosaur fossils, the Danish paleontologist Gerhard Heilmann published his own detailed study in 1926, separating birds from dinosaurs because of this lack of a clavicle^[17] -- a skeletal form which Seeley had also referred to by its trivial name, "merry-thought." (We frivolously call it the "wish-bone".) But Heilmann's tome, rather than Seeley's, set the tone for 20th century paleontology. And, as has been thought by received wisdom until quite recently, for birds to evolve from non-furcular ancestors runs counter to Dollo's law of evolutionary theory. Louis Dollo, following his appointment to the Royal Museum of Natural History in Brussels in 1882, formulated his dictum that evolutionary processes are irreversible, in that once a species has lost a given characteristic it can never regain it. Needless to say, Dollo's law is rarely invoked these days since the exceptions always seem to severely test the rule. For example, as things stand, theropods have since been found which show evidence of clavicles, convincing many in the scientific community of the close relationship between birds and dinosaurs, prompting at least one researcher to exclaim that the dinosaur legacy is alive today in the form of birds.^[18] There's no real argument here, but there is a sizeable range of evidence for further discussion which needs to be addressed. Moon Over Miasma Pangaea Pangaea During the Early Mesozoic -- the Triassic Period -- the continents of Earth were collected together into a single landmass now called Pangaea. This is the overriding reason why similar dinosaur fossils dating from that era are generally considered to be found broadly distributed throughout all the continents. By the Jurassic Period, the single continent was breaking up into Gondwana (in the south) and Laurasia (in the north), and with this split came similar bifurcations of the dinosaur fauna. At the end of the Cretaceous, the continents were rather well-segregated, not entirely dissimilar to what we have today, and with this distribution was a plethora of radically different dinosaur lifeforms. It was also the Age of Giants, as by then most dinosaurs, although by no means all of them, came in sizes of large, extra-large, and enormous. That is, until the Great Extinction. Nonetheless, the preterprimordial question remains as to why and by what mechanism the continents were collected together into the single Pangaean landmass during the Triassic Period and why it broke apart during subsequent ages. The standard answer has been that this was due to tectonic plate movements -- the slow inexorable motion of magma deep within the Earth moving, raising, and subducting landmasses. It's been some 30 years since continental drift became scientifically fashionable with the advent of plate tectonics, after languishing for half a century in the geo-physical dustbin. When German meteorologist Alfred L. Wegener and American geologist Frank B. Taylor independently propounded continental drift circa 1910-11, the idea was soundly criticized despite the persuasive comparison of similarities in transoceanic flora, fauna, and geological formations, mainly because little or nothing was known of geographical outlines of the under-ocean continental shelves or of the mid-Atlantic rift, and even less about magma movement within the Earth itself. It's been speculated that during the late Paleozoic and early Mesozoic Eras, the Earth was rotating much more rapidly on its axis than it is at present. George Darwin, son of the illustrious Charles, had this happy thought over a century ago. This rapid rotation would have the effect of collecting landmasses of a lighter specific gravity than the underlying magma into a single somewhat equatorial Pangaean continent, if not distributing the continent along the equatorial belt due to centrifugal forces. In effect, the continents are something of a slag floating on the more molten underlying asthenosphere. If most of this expanse was to be exposed above sea level, it would act as a nuclear breeding ground for developing land-based lifeforms -- the amphibians that ostensibly came up from the seas during the Lower Carboniferous. A more rapidly rotating Earth would mean that the Moon would have been closer to its primary during these early epochs, whereupon angular momentum would also have to be conserved and the Moon itself would revolve more rapidly in its orbit about the Earth. And, as it is known that the Moon is currently receding from us at a few centimeters per year, this speculation has something other than a remote basis in fact. Moreover, the relatively close proximity of the Moon would have had a more profound effect on magmatic movement within Earth's mantle, most likely with an associated increase in volcanic activity as well as continental rearrangements. This proximity would also have applied to equally profound effects on both land and oceanic tides. As the Moon receded from us over the eons, and Earth commensurably slowed in its rotation, magmatic processes would commence separating the continents, first into large landmasses -- as Gondwana and Laurasia -- and eventually into the continental distribution we have at present. And, conventional thought has it that, with each such separation of landmasses by increasingly larger oceanic straits, lifeforms would also have been separated and isolated so that they could evolve independently. Over the course of the Mesozoic continental redistribution process, the mountain-building mechanism would also have been given additional impetus in areas of tectonic stress. In addition, it has been recently estimated that 97% of the freshwater on Earth is phreatic (subsurface) groundwater, permeating the landmass to varying depths, much of it eventually flowing to the oceans from where it originally came.^[19] If a similar condition prevailed during the Mesozoic, when mountains were first taking shape, there would have been sizeable inland lakes and freshwater seas that would also have been redistributed by tectonic plate movements. Rocks of Ages The fossils of dinosaur bones and animal lifeforms from even earlier eras are often associated with foraminifera-based chalk and limestone laid down in ancient lake or shallow seabeds.^[20] This bespeaks lifestyles that involve seashore or lacustrine habitats, where potable water was readily available for both drinking and as a food source -- for the herbivores and fish-eaters and the carnivores who preyed on the former. This is not to say that all fossils are found in limestone or chalk deposits, for some of the greatest concentrations of dinosaur fossils found throughout the western United States are located in shale and sandstone deposits. Foraminifera, coccoliths, and other chalk-forming plankton laid down strata of their carbonate-based skeletons that are, in many isolated cases, many hundreds of feet deep, such as the cliffs of Dover which are estimated at 1600 feet in thickness. These minuscule creatures also suffered during the Cretaceous catastrophe, as new forms replaced the old species above the K-T boundary. However, for such extensive formations to have come to pass means that this primordial atmosphere was most likely rich in carbon dioxide [CO[2]], as pointed out some 150 years ago by Owen. And yet, today's warm-blooded mammals are known to be adversely affected by elevated levels of carbon dioxide where, as concentrations of CO[2] approach about 4%, they exhibit extreme lassitude and become almost catatonic. Current carbon dioxide content of the atmosphere is approximately 280 parts per million, or roughly 0.03%. (As the Pleistocene or glacial epoch followed the Tertiary Period by some tens of millions of years, no evidence of increased CO[2] would be found in glaciers or ice-core drillings from these much later times.) It isn't known how well reptilian lifeforms fare under heavier CO[2] loading of a breathable atmosphere, and we certainly wouldn't know about dinosaurs; however, birds are extremely susceptible. Some of the evidence for higher levels of carbon dioxide during the Mesozoic is embodied in the so-called greenhouse argument, where solar radiation is trapped in Earth's atmosphere, as tropical or semi-tropical climate during this era is considered to have been far warmer than at present. Tropical animal and plant fossils have been found as far as 70-deg in latitude, both north and south, with a few examples even closer to the poles. This could also mean that most all land masses were then situated more equatorially and not distributed from pole to pole as at present. The cooling of Earth's climate has been tracked throughout the Mesozoic, which some have attributed to the breakup of Pangaea, but it seems more likely that a wholesale reduction of CO[2] contributed to this chilling, perhaps abetted by the massive growth of carbon-hungry foraminifera, as well as the proliferation of plantlife, for coal beds were also being laid down during this period. And, there is at least one other mechanism. As mentioned in another essay,^[21] an increased presence and concentration of carbon dioxide chemically accelerates the cementing process on alluvial sediments without the addition of much heat and pressure. This CO[2] would most likely have come from volcanic outgassing or other venting, and of course be present as a residuum of Earth's primordial atmosphere. And, with any increase in concentration, the gas would act as both a toxic agent and a preservative, as well as a catalytically-inducing concreting factor. Such properties could account for the preservation of intricately detailed flora and fauna fossils that otherwise would quickly have been subject to attack and decomposition by bacteria and other microorganisms. On the Beach Diplodocus Diplodocus "Plant-eating dinosaurs tended to be on the rather bulky side of colossal." (Illustration by Bob Giuliani.) Plant-eating dinosaurs tended to be on the rather bulky side of colossal, and as such required massive amounts of food, particularly if they were endothermic -- warm-blooded.^[22] This also meant that their habitats were not deserts or savannahs, where food availability is sparse at best even for predators. Thus, it isn't without reason that most fossils are found associated with ancient lake beds or shallow seas. But tropical climates are typically associated with rain forests and lush vegetation, ample foodstuff for hungry herbivores, even if their diet was mainly ferns, cycads and conifers, nuts and twigs. And it is the proliferation of flowering plants during the Cretaceous that should have given additional impetus to the plant-eaters. There is a comparative dearth of coprolites -- fossilized feces -- that might afford additional clues to what the feeding habits of these brutes might have been. As near as can be determined dinosaurus were endothermic and had a fully divided, four-chamber heart, separating venous and arterial blood. Living reptiles and amphibians today are ectothermic and have either undivided two-chamber hearts or semi-divided hearts where venous and arterial blood mix. Accompanying such an undivided heart there is also no regulation of body temperature, so that the animal is torpid in cold weather and only active when warmed by an outside heat source. Initially dinosaurs were thought to be like today's lizards and other reptilian lifeforms -- hence their taxonomic name "terrible lizard" -- and so they were assumed to have led rather lethargic lives. However, recent finds seem to have verified that dinosaurs were active, vigilant creatures with an endothermic metabolism that required a voracious appetite to maintain. This does not at all describe reptilian lifeforms as we know them. So, either the early description of the dinosaur as a bipedal or tetrapodal reptile, and of course the image of the flying reptilian pterodactyls, was horribly wrong, or these creatures represented a completely separate genotype from the reptilian order which has survived until the present day. And yet, the climate of their Mesozoic heyday was round-the-clock tropical or subtropical, where efficient metabolic heat-exchangers would have been absolutely essential for the maintenance of body temperature regulation. Under such circumstances, the most efficient "air-conditioning" for sizeable endothermic beasts would have to have been evaporative cooling, and therefore we have to assume that there must have been almost constant breezes circulating around the planet to modulate this cooling effect, else they would have been panting constantly and probably hyperventilating. The horny backplates of the Stegosaurus would act as such a heat-exchanger. Reptilian ectotherms would have no such problem, but then their metabolism would also constrain any sustained strenuous activity. So, one is left with more of a dilemma as to the physiology of these Mesozoic denizens, the climatic conditions during the time in which they thrived, and the constituents of the atmosphere that they breathed. What remains something of an additional mystery, though, is that so many of these dinosaur bones are found with impressions of the outer skin covering fossilized in the surrounding rock deposits. For some of the larger specimens, this is an enigma that calls into question the otherwise assumed presence of impressive amounts of bacteria and other microorganisms which would otherwise have voraciously fed on the carcasses of such animals, particularly in a relatively hot and humid atmosphere. What happened to the evidence -- actual and circumstantial -- for the glut of these microorganisms? The hypothesis has been forwarded, from time to time, that dinosaur species throughout the Mesozoic died from one disease or another. But implied existence of a bacterial or viral infection is not evidential in the absence of microbial proof. It is known that carbon dioxide has an inhibiting effect on aerobic bacteria, while anaerobic microbes can thrive in otherwise alien environments, but over the eons such microorganisms as existed in that day and age should have been acclimated to global conditions and evolved to accommodate climatic conditions, including any environmental changes which may have occurred from time to time. Today, our microorganism population outweighs all other species, both plant and animal, by several orders of magnitude, and comprise both aerobic and anaerobic examples -- there are literally tons of such beasties per acre of land. But, for the Mesozoic, we have scant evidence for their existence, except for what might be entombed in amber fossils along with various insects from that era. Here, again, the absence of evidence is not evidence of absence, but one must be circumspect and exercise care in speculating about what did or did not exist in the Mesozoic. A Touch of Gas Throughout the Mesozoic, with the breakup of Gondwana and Laurasia, there was a general cooling of climatic conditions which some paleontologists believe contributed to the ultimate demise of the dinosaurs, while, as a counterargument, others point to the otherwise anomalous proliferation of speciation during this same time frame. This extensive cooling, however, was rather episodic at best, indicative of catastrophic occurrences that punctuated the Mesozoic. A wonderful popular account of the Chicxulub event, by Walter Alvarez, has just been published,^[23] which nicely supplements Gerrit Verschuur's book.^[24] A climatic drop in temperature can come about in several ways. Cosmologists will sometimes reluctantly admit that the Sun goes through periods of inactivity that result in a cooling on Earth, such as recently occurred during the Maunder Minimum in the 17th-18th century (1650-1710 ad), or events during the glacial ages (Pleistocene Epoch) of the last five million years or so, or the Milankovich orbital cycle, or even that the Sun has now settled down into a more mature stellar, and somewhat cooler, body after a more-or-less exuberant youthfulness. Geologists may point to extensive volcanism dumping ash and other gaseous and particulate debris into the atmosphere that could block out sunlight for extended periods of time, although this is often coupled with the simultaneous movement of tectonic plates, as having occurred during the Mesozoic, accompanied by mountain-building processes. Catastrophists point to the three or four major episodes which punctuate the periods of the Mesozoic, and which may have brought each to a close -- a view which is currently becoming more popular, even among erstwhile uniformitarians. Most geologists and paleontologists are aware of the curious 26,000,000-year periodicity obtained by statistical analysis that characterizes these catastrophes, covering both major and minor events over the geologic history of Earth. (This may vary from 26-31 million years, depending on who does the statistics.) Such long-term cycles are more indicative of cosmic events than of terrestrial ones, and the supposition has been forwarded that a massive solar companion -- perhaps a dwarf or brown star -- that periodically has its periapsis (closest solar approach) somewhere in the Oort cloud of comets, accompanies our Sun at a distance. This would disturb the postulated denizens of the outer Solar System to where an occasional bolide may strike Earth, not to mention impacts on any of the other planets. Another scenario has the solar family passing through cometary clouds every so often, although this wouldn't necessarily be quite so periodic as the 26-million-year cycle. The last such episode would have been some 10-13 million years ago, although there was a minor extinction some 10,000 years ago following the last glaciation. The astronomical community has doubts about the megayear periodicity due to an unseen and undetected solar companion, as there seems to be a tendency of comets to break-up and fall in fragments or clusters such as occurred on Jupiter with the Shoemaker-Levy 9 cometary train in July 1994. It is conjectured here that several factors most likely came into play. Foremost is the hypothesis that Earth had a much more dense atmosphere due to planetary outgassing during the hot Archaean Eon. This would have maintained high carbon dioxide levels in the atmosphere, perhaps throughout the subsequent Proterozoic and well into the Phanerozoic Eon -- an atmosphere that might in certain respects be comparable to that of the planet Venus at present. Most of the CO[2] in present-day Earth is locked up as carbonates in chalk, limestone, and other rocks which, if liberated, would raise our air pressure to 120 atmospheres, some 30% greater than the 90 atmospheres pressure presently experienced on Venus. A proportionately smaller amount of Earth's carbon is stored as coal, oil, and methane. Very little available carbon residue today is actually accumulated as plant, animal, and microbial lifeforms. This means that there was an extravagant abundance of plant if not bacterial life during several periods of Earth's biotic primordial history to accumulate the massive anthracite and bituminous deposits.^[25] But, at least five times during the past 300 million years, significant events brought promising ages to a close with major extinctions. And, with each such episode, Earth may have been struck by an asteroid or comet, the impacts of which would have stripped crucial amounts of atmosphere from our planet and dissipated it away into space. By the time of the Late Cretaceous, we may have had just a fraction of the atmosphere that originally cloaked our planet. Pteranodon Pteranodon. Such "creatures would have been able to more easily take flight and navigate in an atmosphere of greater density than at present." (Illustration by Bob Giuliani.) An extensive atmospheric envelope gives Earth's airmass the property of holding massive additional amounts of water vapor. Since water has a rather high heat capacity, the vapor blanket would also act as a thermal shield, warming the entire planet from pole to pole. Thus, the tropical climate of the Mesozoic over at least 140-deg of latitude would have been effectuated, and the polar regions themselves would have been far milder than at present. This would also mean that both diurnal and seasonal variations in temperature would have been negligible in the middle latitudes. Ectothermic reptiles would have been in their own private paradise, while endothermic creatures would have gasped and panted while seeking cooler environs. Pterodactyls would have spread their furry membranous wings to ride the thermal air currents in search of offshore prey.^[26] The fossilized bones of pteranodon are similar in many respects to those of birds, being light and hollow with internal reinforcing struts and air-sac ducts. The tubular cross-section and reinforcing struts give the bones uncommon strength despite the thin walls, although accidents could easily have damaged this fragile structure. The air-sac ductwork within hollow bones is similar to the lung extension of birds, called pneumatic foramina, and such ducting is found in the larger pterodactyls and should have been effective as a cooling apparatus.^[27] Bats do not have this air-sac ductwork in their bones. Despite their feathers, the primitive Archaeo-pteryx seems to have been more of a glider than the flying pterosaurs which actually flapped their otherwise ungainly wings. Nevertheless, pteranodon would also have been able to open its wings in a mild breeze to become airborne, with occasional flapping to remain at height. Its elongated headcrest would have acted as a rudder for making turns into the wind, while dipping a wing as an aileron would also assist in making such turns. Today's albatross and frigate bird, with their large wingspans and cumbersome mass, need breezy lift assists to become airborne, yet both travel long distances over oceanic expanses with a minimum of wing flapping. Moreover, the frigate bird cannot land on water and become airborne again without the breezy assist, but must roost either on land or the mast of a ship, and use the wind as a take-off advantage. The pterodactyl would have had the same difficulty. But all of these creatures would have been able to more easily take flight and navigate in an atmosphere of greater density than at present. The viscosity of air at ambient temperatures is about 190 micropoises (0.00019 poise). (The poise is a rather large unit of the viscous flow of a fluid, but we'll only be concerned here with comparative viscosities and their simple ratios.) Water at ambient temperatures has a viscosity of about one centipoise (0.01 poise), or some 50 times the resistance to displacement compared with that of air. The viscosity of moisture-saturated air will reduce that of dry air because water vapor itself has a relatively low viscosity -- substantially lower than air. Further, the addition of a few percent of carbon dioxide would reduce it even more, albeit slightly. And, if the density of such air was doubled or trebled, or, for that matter, even if the pressurization was increased an order of magnitude or two, viscosity would not increase linearly with pressure.^[28] (The compressed air in a steel cylinder at 2500 lbs. per square inch is 170 times that of normal air pressure at sealevel -- 14.7 lbs psi -- but it is still far, far more fluid than liquid water.) The viscosity of gases increases with temperature up to about 400 atmospheres pressure, after which it tends to drop somewhat, while that of liquids tend to decrease with temperature irrespective of pressure. Boiling water, for example, is 70% more fluid than ice water. And, in an extreme example, for a gas such as carbon dioxide at about 450-deg C on the surface of planet Venus under enormous pressure, the viscosity would nominally be in the neighborhood of 400-500 micropoises. Not that anyone would want to fly on Venus, it does point out that this viscosity is still far below a value that would make flying difficult. This, of course, doesn't constitute a persuasive argument for a more massive atmospheric envelope in Earth's primordial past, but what this means in terms of pterodactyls being able to flap their wings and fly in Earth's primordial atmosphere is simply based on the fact that they and their progeny were able to do so for 50 million years. Indulging in Hyperbole Rhamphorhynchus Rhamphorhynchus. Magnificent pterodactyls which once soared like dragons eventually flew no more. (Illustration by Bob Giuliani.) If the seemingly periodic extinctions throughout geologic history were due to meteoric impacts with the concomitant loss of atmosphere, sudden reductions in air pressure on the planet could initiate tectonic disturbances and associated volcanism due to surface expansion as internal magmatic pressures would be relieved by the expulsion of atmospheric overburden. The shock waves during the primary impact of sizeable bolides would add kinetic thermal energy to the frictional heating during the brief moments of passage through the atmosphere, initiating numerous firestorms in its wake. Overheated gases in the upper atmospheric strata would boil away and be lost to space, being then wafted away on the solar wind. Once explosive volcanic activity commenced on the surface, the resulting dust and gas loading of the atmosphere would at first contribute an additional thermal burden to the airmass. Then, with the encroaching darkness from the opaque dust clouds blotting out the Sun and radiating their heat energy into space, a cooling would be initiated that would precipitate the atmospheric-entrained water vapor in torrential rains that could last for weeks, creating flash floods to wash the lowlands and meadows free of vegetation. This precipitation would contribute to, and further enhance, the cooling effect until an equilibrium of sorts is once again restored. A single such occurrence in Earth's history could conceivably alter the direction of developing species. Several such occurrences spaced over the eons would certainly be expected to do so. The last catastrophe at the end of the Cretaceous would have left an almost desert planet. It must have been far more extensive than the description of an impact of a single 10-kilometer bolide in Yucatan, although it has been suspected that this K-T event may have been part of a meteoric train. However, of all the logged major and minor catastrophes sprinkled throughout paleontologic history, most apparently did not result in wholesale decimations of lifeforms. But, following this Late Cretaceous event, the atmosphere would have become considerably thinner but breathable, the oceans a little more muddied and salt-laden but livable, and the gradually drying land barren of vegetation but still comparatively fertile. After the firestorms and inundations which devastated the planet had subsided, plantlife would have become scattered and scarce, and the sprouting of remaining seeds and spores would have taken several seasons to germinate, to once again take root, and then to spread. The surviving ornithopods and sauropods which previously thrived on the unrestricted proliferation of these plants, coupled with a lack of drinkable water, would have starved and become desiccated with thirst. And, the predatory theropods which somehow endured and fed on these creatures would have found fewer and fewer meals. The end would have come quickly for what sole survivors remained after the cataclysm. The magnificent pterodactyls which once soared like dragons, scooping up a meal of fish or plankton from the shallow seas they knew so well, would have flown no more. They would have died, one by one, in the very lake mires where they had once fed, to be eternally blanketed by the indifferent silt laid down by new generations of mindless foraminifera. And then the mammals would have come out from their furtive hiding. Notes ^[1] D. Norman, Dinosaur! (N. Y., 1991), pp. 74, 218. ^[2]Previously, I myself had entertained weight overestimates which have since become outdated. See, F. B. Jueneman, Limits of Uncertainty (Chicago, 1995), p. 17. ^[3]But see, C. W. Hunt, "Anhydride Theory: A New Theory of How Petroleum and Coal are Generated," elsewhere in this issue. Ed. ^[4] D. Norman, op. cit., p. 47. ^[5] R. T. Bakker, The Dinosaur Heresies: New Theories Unlocking the Mystery of the Dinosaurs and their Extinction (N. Y., 1986), pp. 48 ff. ^[6]D. Norman, Prehistoric Life: The Rise of the Vertebrates (N. Y., 1994), pp. 134-141. ^[7]A. J. Desmond, The Hot-Blooded Dinosaurs (N. Y., 1976), pp. 146, 200. ^[8] Ibid., p. 198 (emphasis added). ^[9] L. W. Alvarez, et al., "Extraterrestrial cause for the Cretaceous-Tertiary extinction,"Science 208, (1980), pp. 1095-1108. ^[10]G. L. Verschuur, Impact: The Threat of Comets and Asteroids (N. Y., 1996). ^[11] A. J. Desmond., op. cit., p.195. ^[12]E. H. Colbert, The Age of Reptiles (N. Y., 1966), pp. 62-63. ^[13] R. T. Bakker, op. cit., p. 258. ^[14] E. H. Colbert, op. cit., p. 101. ^[15] R. T. Bakker, op. cit., pp. 293-5. Cf. also J. F. Bonaparte, "Pisanosaurus Mertii Casamiquela and the origin of the Ornithischia" Journal of Palaeontology, 50 (1976), pp. 808-820. ^[16]H. G. Seeley, Dragons of the Air: An account of extinct flying reptiles(N. Y., 1901/1967). ^[17]G. Heilmann, The Origin of Birds (London 1926). ^[18]C. McGowan, Dinosaurs, Spitfires, and Sea Dragons (Cambridge 1991), p. 318. ^[19] K. A. Svitil, "Groundwater Secrets,"Discover (September 1996), p. 28. ^[20] A. J. Desmond, op. cit., p. 188. ^[21] See, F. B. Jueneman's critique of D. Dennett's Darwin's Dangerous Idea, forthcoming in a future issue of AEON. Ed. ^[22] C. McGowan, op. cit., pp. 129ff. ^[23]W. Alvarez, T-Rex and the Crater of Doom (Princeton, 1997). ^[24] See reference #10. ^[25] But see, C. W. Hunt, "Anhydride Theory: A New Theory of How Petroleum and Coal are Generated," elsewhere in this issue. Ed. ^[26] D. Norman, op. cit., p. 140. ^[27] C. McGowan, op. cit., pp. 283-284. ^[28] M. A. Benning to F. B. Jueneman (May 23, 1997), private communique. Cf. also, I. F. Golubev, Viscosity of Gases and Gas Mixtures (Moscow, 1959), pp. 76ff.